The use of double needles for the withdrawal of blood is widely known and accepted. Such needles may be manufactured to be integrally formed with a syringe barrel or they may be manufactured separately with external threading so that the double needle may be secured into the end of an appropriate syringe barrel. A typical double needle of the latter type is marketed under the trademark VACUTAINER which is owned by the Becton Dickenson Corporation.
With both the integral unit and the separate double needle, both needle configurations are the same. Namely, one needle extends upward centrally into the syringe barrel while the other needle extends in the opposite direction, outwardly from the syringe barrel. The latter needle is used to accomplish the vena puncture.
In the manufacture of these needles the only concern for the gauge of the needle is that the needle which extends into the syringe barrel must be sufficiently rigid to puncture the rubber test tube stopper without the needle bending or buckling. The needle which is used to accomplish the vena puncture has previously no been a concern and it is typically of a standard blood withdrawal size which is between 12 and 16 gauge. These gauge sizes are of the type typically used for blood donors, who by law must be of at least a certain age and are generally not frail or infirm. The automatic transfer of these needle sizes from such a use to a use on patients who may be young or may be frail, fails to recognize a major disadvantage of the double needle vacuum tube blood withdrawal systems presently in use. Some double needle systems are scaled down for use with small syringe barrels where only a small sample of blood is required. In these scaled down systems the needles may be approximately 21 gauge.
The gauge of the needle refers to standard wire gauge measurements and defines the outer diameter of the needle. The inner opening of the needle is generally not defined but relates directly to the gauge and the use of either a thin wall or standard wall needle which are well known in the medical field. For the purposes of this application the commonly used gauges will be utilized. It should also be appreciated that either a thin wall or standard wall may be used without significantly effecting the actual opening of the needle and the flow rates of the blood passing therethrough.
In use, one or more vacuum test tubes are placed in proximity to the patient and may in fact, be placed within the syringe barrel with the stopper of the test tube near or against the tip of the second (rear) needle, but without the rear needle piercing the stopper or disrupting the vacuum seal. The first (front) needle is then used to accomplish the vena puncture which would result in some blood traveling through the needle toward the syringe barrel at a relatively slow rate, as determined by the pressure within the patient's vein. Once the vena puncture is accomplished, the test tube is advanced into the syringe barrel until the second needle pierces the test tube and the vacuum in the test tube quickly draws the blood through the needle and into the test tube. It is common that during this initial puncture the blood will initially squirt into the test tube and against the test tube wall. As the pressure within the test tube and that within the vein seek equilibrium blood fills the tube which blood acts as a cushion for the new blood entering the tube.
For these systems to work properly the test tubes must have a sufficient vacuum to draw enough blood into the test tube for future testing. To accomplish this and due to difficulties that exist should a test tube be used which does not have sufficient vacuum pressure, the tendency is to create more of a vacuum within the tubes than is actually needed. The purpose of this being to avoid the situation where additional vacuum tubes have to be used to obtain a sufficient amount of blood to accomplish the desired testing. Also, one of the main purposes of this system is to reduce the direct handling of the blood and thus, separate test tubes are generally used for separate tests and if a particular test tube does not withdraw enough blood to accomplish that test then that test tube and the blood is simply discarded and a complete new test tube for the desired testing is utilized. One can appreciate the type of frustration and difficulties that would result if a tube or several tubes in a row did not have a sufficient vacuum to withdraw the necessary amount of blood for testing.
The results of this manufacturing process, which seeks to make the test tubes with a significant vacuum, is that when used, there is an initial pulse of blood as maximum suction is applied at the first piercing of the stopper. With the use of these relatively large gauge needles (12-16 gauge) this initial pulse actually squirts the blood into the test tube. When this initial blood impacts in the test tube there is a measurable amount of hemolysis. Whenever hemolysis is created in the blood sample there is a skewing of the test results because there are now less red cells due to their hemolysis and the contents of the now hemolysized red cell are floating freely within the sample.
When the patient has veins which are relatively healthy and resilient there is no difficulty in the vein absorbing a number of vena punctures from these large needles with no adverse effect. However, where the patient is an infant or if the resiliency of the vein has been diminished due to age or illness, numerous vena punctures can cause vein blockages which has a detrimental effect on the treatment as additional veins must be located and used in order to maintain the necessary monitoring. This problem is further exacerbated in those situations where blood needs to be drawn frequently to monitor the patient's progress or condition. In these latter situations it is not uncommon for the patient to virtually exhaust their supply of suitable veins for the withdrawal of blood. In fact, it is not uncommon that a person with fragile veins and requiring numerous blood withdrawals and/or transfusions may have only one or two veins that are suitable for the easy withdrawal of blood. In these situations, the blockage of a vein may require surgical procedures in order to obtain access to a vein for obtaining blood samples.
It should be noted that it is common for the prior art to disclose in the drawings, a possible size variation between the rear needle and the front needle. This occurs because in some situations the rear needle which punctures the stopper is of a gauge which is too large for a vena puncture on even a healthy person. Thus, while some size variation may be disclosed in the drawings there is no disclosure of the problem addressed by the subject invention and no disclosure of the parameters necessary to achieve the solution to that problem.
By transferring the same size vena puncture needles used when healthy people donate blood to hospital usages where the patient has fragile veins disregards the physician needs to obtain as accurate blood data as possible and to care for the blood source and seek to obtain vein longevity. It was with these ideas in mind that I sought to maintain the present system which has the advantages of limiting blood contact while reducing the negative effects of the present system to an acceptable level. The subject invention is the result of these efforts.